Fuel control for a twin spool gas turbine engine



Jan. 15, 1963 w. H. cowLEs ETAL 3,073,115

FUEL CONTROL FOR A TWIN SPOOL GAS TURBINE ENGINE Filedv March 18, 1959 2Sheets-Sheet 2 /4 /o 22w i 30 -E 5;28 Z? 2o I 58 /lgg l i 70/d o l I/4`l2a I United States Patent 3,073,115 FUEL CNTROL FR A TWHW SPOL GASTURBINE ENGINE Warren H. Cowles and Dean F. Wheeler, Detroit, Mich.,

assignors to Holley Carburetor Company, Van Dyke,

Mich., a corporation of Michigan Filed Mar. 18, 1959, Ser. No. 800,300 4Claims. (Cl. 60-39.16)

This invention relates generally to fuel controls, and more specificallyto fuel controls for turbine engines.

Gas turbine engines may be classified broadly into three groups such as(l) turbojet, (2) turboprop and (3) turboshaft. The turbojet engine isone which relies upon jet thrust to develop its propulsive force,whereas, a turboprop has its turbine shaft coupled to a propeller, aswell as to the compressor, so as to develop its propulsive force byslightly increasing the velocity of a large mass of air. The turboshaftengine differs from the turboprop in that the turbine shaft is coupledto an output shaft which drives something other than a propeller. Thisoutput shaft may, for example, be a drive shaft for a land based vehiclesuch as a truck.

Each of these engines, although identical in many basic concepts,require different types of fuel controls. That is, they may requiredifferent methods by which the speeds of the related components such ascompressor, turbine, propeller, output shaft, etc. can be detected and/or regulated.

In view of this, it is now proposed to provide a fuel control which canbe readily adapted to ay turboprop, turboshaft or turbojet enginewithout the necessity of any major rework with the possible exception ofonly minor changes in calibration.

vOther more specific objects and advantages will become apparent whenreference is made to the following specification and illustrationswherein:

FIGURE 1 is a schematic illustration in cross-section of a fuel controlembodying the invention, as used in conjunction with a typical turbopropengine.

FIGURE 2 is a fragmentary view in cross-section illustrating the minorchanges required to adapt the fuel control illustrated in FIGURE 1 to atypical turboshaft englne.

Referring now in greater detail to the drawings, FIG- URE 1 illustratesa turboprop or as sometimes called free-shaft turbine engine whose fuelsupply is controlled by the scheduling type of fuel control 12 embodyingthe invention. The engine 10 has a housing 14 with an air intake 16 andexhaust nozzle 18. A combustion chamber 20 having a fuel distributionring 22 therein, is located within the housing 14 between the compressor24 and turbine 26. The power plant illustrated is of the split turbinetype which has its forward turbines 29 (compressor turbines or gasproducer turbines) driving the compressor by means of a hollow shaft 28.The free turbine 27 drives a propeller, or, in the case of aturbofanengine, a fan 32 by means of a second shaft 30, concentric with 28, anda gear box 34. Since turboprop and turbofan engines are basicallyidentical, it is evident that all considerations necessary for asuccessful fuel control for a turboprop would be the same as those for aturbofan fuel control. It is of course to be further understood that theinvention is not limited to just this particular type of turbopropengine. l

The fuel control 12, having ahousing 36, contains a fuel inlet conduit38 which in turn contains a pressure responsive valve 40 therein. Asecond contoured Valve 42 allows the fuel to flow to the main meteringvalve 44 in accordance with its position with respect to the meteringsurfaces 46 as determined by the pressure sensing means 48.

3,073,115 Patented Jan. 15, 1963 ice biased to the left by a spring 52and a spring retainer 54 l monuted on one end of the bellows. l'hechamber 56 which houses the pressure responsive means 48 communicateswith a pressure probe 58 located within -the power plant. Generally, theprobe senses some compressor pressure; however, for purposes ofillustration the probe is shown in a position to sense compressordischarge pressure Pta although it could sense any intermediatecompressor pressure. A member 60, rigidly secured at its opposite endsto valve 42 and the free end of bellows 50 serves to more the valve 42in accordance with the position of bellows 50.

Chamber 62 houses a double diaphragm valve 64 which is comprisedgenerally of a double ended member 66 having diaphragms 68 and 70secured thereto. The diaphragms, among other things, serve to divide thechamber 62 into three distinct and variable chambers 72, 74 and 76.Chambers 76 and 74 contain springs 78 and respectively which bias themember 66 for purposes of calibration. Chamber 76 communicates vwithconduits 82 and 84, while chambers 72 and 74 communicate respectivelywith conduits 86 and 88. An arm 90, secured at one end to member 66 andpivotally mounted at its other end at 92 is rigidly secured to a servovalve 94 which cooperates with a seat 96.

A temperature sensing and compensating mechanism 98 is illustrated ashaving a three dimensional cam 100 which is rotatably positioned bymeans of a sha-ft 102, arm 104, lever 106 and a temperature responsivebellows 108. The temperature bellows of course derive their force fromthe expansion and contraction of the fluid which is sealed Within thebellows 108 and temperature probe 110. A slotted member 112, pilotedwithin the chamber 114 and secured to the earn 100, cooperates with theextended portions 116 of shaft 102 to rotate the cam in accordance withthe temperature.

The other side of cam 100 is connected to a piston 118 which is biaseddownwardly by a spring 120. Chamvber 122, which contains piston 118,communicates with the pressure P2 in conduit 124 while chamber 126 onthe other side of piston 118 is at a pressure P6. A hydraulic balancedvalve 125, biased to the right by a spring 128, has a metering edgecooperating with the edge 132 to cause a pressure differential betweenchambers 134 and 136 which is a function of the position of cam 4' Twohydraulic speed sensing 4units 138 and 140 are connected to the turbinepower plant at different points, The speed sense 138 is connected to thegas producer portion of the engine by means of transmission 142 and gearbox 144; whereas, speed sense 140 is connected tov the free turbine 27by means of gear box 146. The speed sensing unit 138 is substantiallycomprised of a generally tubular center portion 148 which has securedthereto a pair of radiallyformed members 150 and 152. Member 150contains a valve 154 which is normally urged radially outward by thebiasing force of spring 156. The valve 154 is adapted to control theduid ow through port 158 which is formed within member 150. A threadedspring seat adjustment and counterweight 162 may be .provided withinmember 152. A generally cylindrical chamber 164 surrounds the members150 and 152 as they are rotated by the central tubular portion 148 andtransmission 142. The speed sense 140 is similar in all respects to thespeed sense 138; however, for sake of clarity the elements comprisingunit 140 that are like or similar to those of unit 138 are identifiedwith the same numerals followed by a letter a suflix.

Generally, the main fuel metering valve 44 is con- .toured toprogressively increase fuel flow in accordance tions of-valve-44, otherthan minimumow, are def terminedf byy the lcoll'ective 'actionV of f thepressurel responsive members'163 and 170. y n

The` member 16S= is' comprised of` a main bodyl porvtiong172; 'having apilotV at one endv and a diaphragm 174 secured to its .-otherend, and aspring; 17e resiliently urging thebod'y172r` and diaphragm` to theright. Member--170 is similar tofmember 168 inV4 that it alsohas apiloted bodyV portion-,178, diaphragm 180'y and a spring- 18'2. However,an important difterence'i'sthat the spring pad 18`4fforspring 132 ismovable, whereas lthe pad for spring y176 is vxed. The movable pad 1h41isy pivotallyl secured to an arm 136 which has aroller 183 in contactwith a cam 1-90; The .other end-of arm 1&6' is pivotally secured'to thehousingf.' Y

1A levery 192,` pivotally and slidably received at its loplpositeendswithin-openings 194 and 196 formed in v bodyg'portionsV 172v and 178,is-pivotally secured to the main metering valve 44s f f Abean-slotted'cam 193issecuredto the power src-- lectorshaft 2)0fwhich has secured toyit, at itsopposite ends, cam Y19t)L andthe manually positioned selectorlever 211);v Thegcam `19.3Ais--used-to actuate the cooperating rod 212whichcloses thevalvemember 2142011 engine shut down. Valve member 214,when closed, is to the` right,- thereby preventingfurther fuel howthrough the outlet port 216i tothe engine fuel manifoldring- 22.

A' mauiinmmV pressure valvey 213 is provided with a spring=22t urgingitin adownward position; As the pressure within conduit 38 increasesabovel the design sure P2 is then communicated tochamber 76, by meansVof conduit 32, and subsequently to conduits S4: andnlZLi 1 limitsyvalve'218,1by`virtue of its communication with conduit. 38; through port-222,'is forced upwardly against spring; 220 so as-.to allow fueltorreturnto the intake side.l oit"v pump 224. AmaXimurn-fuellimiter'valve 226 is alsosresiliently urged downwardly byeVspring 228. As` Y Vfuel flow tends'f to exceed safe values, the valve226, in

cooperationy withgtheservo valve 94, bypasses thefexcess fuelto.the-"r'eturndine 230.` The lexact mannerv of'operation.\villbef..n1orefullyk discussed'v later in thespeci-` cation.

OPERATGNl AL brief discussion ofj the functioning ofthefuel con-r. trolLduring steady "state engine operation 'will' be presentedrfirst inorder Vto illustrate .the precise, functions. of" theindividual'icomponents.

Fuel at a pressure of Plis delivered by the lpurnpgZZi' tothe inlet38whichcommunicates with aconduit 232.

Afre'striction234tplacediwithin conduit'23l2 causes a pres-.

` byh means 'of4 conduit-246` which is incommunicati'on .with chamber164i.'- Conduit 23.6, branching oi from. conduit4 232.A 'anteriory ofrestriction 22,4v and communicating with chamber 164a'and chamber 23S/bymeans of conduit 2.46,

A has-a restriction 242th1ereinV which causes the'pressure. P1.

to'-` goto some value P7 'in both of` said 'chambers'.

'PressuresiPe and Pq are each determined inalike'mauner'by'speedsensesf138 and 140, respectively. Forex;

ample, at relativelyl low rotational speeds of tubuiar por# vtion'-148'and arm members 150 and 152,V pressure; P6. forces'fvalve 154Vinwardly toward'the center of rotation against, the resistingforce'ofispring 156.1 Consequently,

. ow takes'plaee quite readily through orifice, 153; past valve-:15,4and* into the cavity. 259u which is ata p ressure P2.

Because of the low-resistance to ow through orifice .1158,vtheapressurePg approachesl the(4 lower pressure Pg in` 4 value; However,as' rotational speed of memberv148l increases, due to an increase ofcompressor speed, the centrifugal force of valve 154 increases causingthe valve to more nearly close oi the orifice 158. Since there is now agreater restriction to ilow through orifice 15S, pressure PG increasesand approaches the higher'pressure P1 as an absolute limit. In thismanner, it is possible to obtain a hydraulic pressure signal which isindicative of speed. Generally speaking, the higher the speed, thehigher pressures P5 and P7 become'. Pressure P6 is communicated togovernor diaphragm chamber 244 by means of conduit 24M, while pressureP7 in chamber 16411 is directed to governor diaphragm chamber 23S? bymeans of conduit 240.

Fuel at pressure P1v is also directedY past valve 49,wl1ich maintains arelativelyk constant pressure drop, into-chamber 24h where it exists ata new pressure P2. The preswhich communicate with chambers 251i and 122irespectively. Conduit 252, which` intersects. conduit S4, serves tocommunicate the pressure P2 to. chamber. Za of'speed` sense v111i) andchamber` 254 tothe left of'v diaphragms 174 and 1&0.

The fuel. atapressure'P2 is then directed past the contoured valve ft2,which cooperates with the metering surfaces. t6 to produce a variablepressure. drop resulting in a pressure P3. in conduit 256. is determinedby the compressor discharge pressure Pm. Generally, as compressor.discharge pressure increases, the pressure. drop-across the valve.d2tdecreases, causing P3 to increaseand approach P2. communicated tochamber 72 by means or conduit 36.

Conduit 8S, communicating between chambers 74 and 136, conveys fuelat apressure. P2A which resultsfrom the pressure drop across metering edges13G.- andf V132fwhen the valve 125 is moved to some position by` cam166;

Chamber 13.4, which communicates with chamber'lZt, A

is--at a pressure P6 which. isv greater than P8. A conduit 253hydraulically connectingfconduit S'wth conduit 124. has .a restriction26) therein which, in effect, determines theV pressurer dilerentialwhich may` exist between P2l .thereby determining P3, and cam 160 willhave moved.

axially in accordance with ther pressure dierential' bef tween P2 andP6. Furthermore, the cam 16) will be angularly adjusted in accordancelwith temperature by means of probe. 110bellows-` 198, and linkages 106,1de, m2 and 112. The position of'cam ttfdetermines the position ofvalve/125, and consequently Pain chamber '74. Pgisof course greater thanP2.or P3.

Pressure P6.. determined by'speed sense 138, is directed againstdiaphragmr 180 while pressure Pq, determined by"v speed sense 140, isapplied to diaphragm-.174. TheV two pressures, independently of eachother, urge their respective,,diaphragmsv and` members 172 and-178.` tothe left., However,v it lshould beyclear,l evene. though the actions.are independent ofA each other, lthat thenal move-Y ment impartedtovalve 44 mayv be, due tor the eolleetive actions of the members-172 and178. It can readily be seen that the speedsense. can override the speedsense 1 38. That is, if the powen turbine should overspeeddue possiblyto some change in propeller pitch, the .speed sense 14h will reduce fuelow tothe-burners by more nearly closingV off the valve 44. In thismanner, the

lspeed of the power turbine is reduced and-consequently the speed of thepropeller is maintained within safe limits.

Engine Acceleration Generally, the fuel control also operates asoutlined above during conditions: of' acceleration. However, afew of theelements makingup the control are positioned'differently.l As'more poweris'dernanded, the operator rotates the power selector lever 210counter-clockwise, there` The'position of valve 4t2-r' The pressure P3.is also by rotating cam 190 so that follower 18S-is urged to the right.This causes the spring pad 184 to compress spring 182 in a manner so asto oifer greater resistance to the force created by P6. Member 178 ofcourse moves to the right during this time, causing the lever 192 andvalve 44 to move to a more nearly open position. When the desired poweris obtained, P6 will again become sufficient to establish a condition ofequilibrium with spring 182 and P2.

The maximum operating line or acceleration line (acceleration fuel ilowplotted against engine speed) is determined by the action of servo valve94. Once the operator selects an increase in power, valve 44 is moved toa more nearly fully open position to allow a greatly increased fuel owto the engine. However, the engine cannot take an unregulated increasein fuel flow, but must take it according to a schedule determined bycertain parameters. These parameters, in the case illustrated, arespeed, temperature and Pm. The mechanism 9S is provided in order todetermine the desired fuel flow upon acceleration, for all engineoperating conditions.

The mechanism 98 accomplishes its purpose by determining the pressureP8, which is representative of desired fuel iiow, and comparing itagainst the actual fuel ow past valve 42 as sensed by the pressuredifferential P2-P3. Whenever the actual fuel flow becomes too great, themember 66 is moved clockwise about pivot 92, therebyopening servo-valve94 some amount off of seat 96. It should be pointed out at this time,that the servo 94 is actuated only during periods of acceleration.

In order to more clearly explain the operation of member 66 and servo94, let it be assumed that the engine is under a condition ofacceleration. During this time, the rotational speed of tubular member148 is increasing thereby causing pressure P6 in chamber 126 to increaseand move cam 160 upwardly. As cam 109 so moves, valve 125 is moved tothe left causing a greater restriction to flow from chamber 134 tochamber 136. Additionally, if the temperature increases, probe 110 willmove valve 125 further to the left by means of cam 100. Consequently,P8, which is directed to chamber 74 is a function of the speed andtemperature and the differential of P8 to P3 is used as an indication ofthe desired fuel ilow to the engine.

Contrasted to the signal is the one indicating the actual fuel flow.That is, the pressure differential of Pzto P3 is an indication of theactual fuel flow past valve 42.

The differential of P8 to P3 is placed across diaphragm 68 while thedifferential of P2 to P3 is placed across diaphragm 70 which is largerthan diaphragm 68. Accordingly, whenever the force created by the actualfuel flow past valve 42 becomes too great, and unbalances the forcecreated by the desired fuel flow, servo valve 94 is opened I and anappropriate quantity of fuel is bypassed by valve 226.

Conduit 262 which communicates with conduit 257 is, during periods offlow, at a pressure P5 due to restriction 264. Conduit 26e hydraulicallyconnects one side of valve 226 to conduit 262 and is at the samepressure P5. Therefore, as servo 94 opens in accordance with the signalinput of the computing mechanism 98, P5 drops due to the flow by servovalve 94 to the cavity pressure P9. This results in valve 226 beingforced open due to the pressure P2 of chamber 24S overcoming thecombined force of spring 228 and pressure P5. This in turn causespressure P2 to drop some amount; however, the valve 44 is not affectedby this drop,.since both P6 and P7 drop accordingly and the resultingpressure differential remains a true indication of speed. Therefore, asvalve 226 opens, fuel is bypassed back to the tank in accordance withthe maximum acceleration line determined by the mechanism 9S.

Engine Deceleration When less power is demanded, the operator rotateslever 210 clockwise, allowing the valve 44 to move to its furthermostposition to the left. The point at which the motion of valve 44 isarrested depends on the placement of the minimum ow stop member 166'.The member FIGURE 2 illustrates in fragmentary crosssection the4adaptation of this invention to a turboshaft engine. The elements whichare like or similar to .those of FIGURE 1 are identified with likenumerals. From a comparison of FGURES l and 2, it will be seen thatconduit 236, which formerly communicated with chamber 164a of speedsense 140, is replaced with a conduit 236m which communicated withchamber 164g of speed sense 140, is replaced with a conduit 236:1 whichcommunicates with chamber 164 of speed sense 138. Conduit 2401, however,still hydraulically connects conduit 236:1 with chamber 233. Speed sense140, as in FIGURE 1, communicates with chamber 254 and conduit 84 bymeans of conduit 252; however, the chamber 164a now communicates withchamber 244, instead of 238by means of conduit 24651.

tails and exterior connections are the same as betweenf the turbopropand turboshaft versions of the fuel control. This is achieved by thevuse ofy small cap members 272 and 274 of FIGURES l and 2, respectively.When 272 is used, the hydraulic network within the control is such thatthe operator, when selecting a power lever angle, actually preselects adesired compressor 24 (gas producer) speed. if adapter member 274 isused, the hydraulic network is changed so that the operator selects adesired output'shaft 263 speed by positioning the power lever 210.

If a power plant is to be used as a turboprop, the speed ,which `isselected must be that of the compressor, `slnce this will determine thepower of the power plant. The speed sense connected to the propeller orpower turbine is used strictly as a propeller overspeed device -whichwill reduce the selected fuel flow to the burners 1n o rder to bring thespeed of the propeller and power turblne within safe operating speeds.Therefore, it -becomes apparent that in a turboprop engine the fuel is4basnally metered in accordance with the compressor spee If, however, apower plant is to be used as a turboshaft, the speed selection must bemade with reference to the output shaft. In this case, the speed senseconnected to the compressor is used as the overspeed device; this willreduce the fuel flow to the engine when loads are suddenly reduced onthe output shaft, preventing output shaft and possibly compressoroverspeeds. In view of this requirement, it follows that the fuel isbasically metered in accordance with the output shaft speed and load ina turboshaft engine.

Many engines which are designed to be used as turboprops are capable ofbeing used, with slight modications, as. turboshafts. A fuel controlwhich is designed for one will have the same physical requirements as tospace, weight and location at if designed for the other. Therefore, itbecomes evident that a fuel control constructed in accordance with thisinvention is capable of adapting itself to either type of engine withoutthe necessity of relocating or changing any major components, except forthe small hydraulic adapter members 272 and 274. If the fuel controlwere'not constructed according to the invention, it would be necessaryto relocate various speed sensing devices and change the internalhydraulic cirparticular engine; this would mean ,that a fuelcontroldesignedfor aturboprop could not be used with a turbo- Vshaft powerplant.

A turboprop and turboshaft application of the invention havebeendiscussed in order to more clearly illustrate the extreme conditionsof which the invention is capable of adaptation. It is of course,apparent that theconsiderations for a turbojet engine would be like thatfor the turboprop illustrated in FIGURE 1.- Accordingly,` if theinvention were to be used on a turbojet engine, the various connectionswould be made as also illustrated in FIGURE 1.

Although but yone embodiment of the inventionhas been disclosed, it isapparent that other modifications are possible within the scope of theappended claims. What we claim as ourV invention is:

amants L Al fuel control for afree-shaft turbine engine having Y a freeturbine anda compressor with a driving turbine therefor, comprising ahousing, an unmetered fuel inlet and .a metered` fuel outletin saidhousing, a conduit connecting said inlet and outlet, a variable orificevalve member adapted to variably restrict the fuel flow throughsaidconduittin accordance with compressor pressure, a second valvemember adapted to meter the fuel fiow through said conduit in accordancewith compressor speed,

a pressure responsive unmetered fuel bypass valvecon` duit meansdirecting a pressure signal created in lpart by metered fuel pressure tosaid pressure responsive bypass valve, a `servo valve adapted to attimes reduce in varying degrees the magnitude of said pressure signal,and a force balance system responsive to the fuel fiow past saidvariable Yorifice valve member for controlling the adapted to variablyrestricttthe fuel fio'wvthrough said conduit in accordance withcompressor pressure, a secondvalve member downstream; of said firstvalve member s and adaptedl tofmeter the fuel flow through said'conduit"r 1nl accordance with compressor speed,wa pressure responsiveunmetered fuel bypass valve, conduit means directa pressure signal;created in part by metered'- fuell pres--l l sure to saidfpressureresponsive bypass valve, a servo valve adapted to at` Atimes reduce invarying degrees the magnitudev of saidy pressure` signal, and aforcebalance system responsive to both the fuel ow past said first valvemember and compressor speedl for controllingthe position, of saidservovalve.,

3. A fuel control fora free-shaft turbine engineA hav-V in g Iafreeturbine and -a'co-mpres'sor with al driving turbine' therefor,comprising a housing, an unmetered fuel inlety and a metered, fueloutlet-in said housinga conduit connecting saidinlet andyoutlet, a firstvalve member adaptedf` fto-variably.- restrict the fuel flow. throughsaid conduit in.' accordance withcompressorsdischarge pressure, asecond-l` Vvalve member downstream of said firstv valve member andjyadapted to meter'therfuel flow through. said conduit in aecordance withcompressor speed, .a pressure responsiveI unme'teredfuel bypassitvalve,conduit means directing 1a pressure signal. created in part by meteredfuelY pressure to said pressure responsive bypass valve, a servo v .alveadapted to at times reduce in Varying degrees the magnitude of saidpressure signal, a force balance system responsiveto both` `the; fuelflow past said first .valvemember and; compressor-speed for controllingthe position of` said servo,` valve, and temperature responsive meansfor-varying they effect of said compressor speed-on said f orce balancesystem inA accordance with temperature-.-

Y 4, aginal.,controlfotatteershaft turbineensne haring;

a free turbine and a compressor with a driving turbine therefor,comprising a housing, an unmetered fuel inlet and a metered fuel outletin said housing, a first conduit connecting Said inlet and outlet, aspring loaded valve inv said conduit, a spring biased. fuel bypass valvecommunicating with said first conduit upstream of saidtrspring4 loadedvalve, a variable orifice valve member in said conduit downstream ofsaid spring loaded valve, VErst pressure responsive means responsive tocompressonpressure and operatively connected to said variable orificevalve member for positioning said variable orifice valve member in4accordance with'compressor discharge pressure, an acceleration fuelbypass valve communicating with said first conduit intermediate of saidspring loaded valve and said variable orifice valve member, a variablypositioned governor valve in said first conduit downstream of saidvariable orifice valve member, rst andr second centrifugally positionedvalve means for creating a first and second hydraulic signalindicativeof the yspeed of rotation ofY said free turbine and compressorrespectively, second and third pressure responsive means yconnected tosaid governor valve, a second conduit communicating between said firstcentrifugally positioned valve and said second pressure responsive meansin Ia manner so as todirect saidy first pressure signal to said secondpressure responsive means and thereby position said governor valve inaccordance therewith, a 4third yconduit communicating betweensaid-second,centrifugally positioned valve and said third pressureresponsive means in a manner so as to direct said second pressure signalto said third pressure responsive means and thereby position saidgovernor valve in accordance therewith, a pressure responsiveservo'valve for controlling the position of said accelera- Y tion fuelbypass valve, a fourth conduit communicating relatively high fuelpressure and adapted to direct said' pressure to .said servo valve, Kasecond variable orificev valve ymember for controlling the fiow throughsaid sixth conduit and consequently determine the magnitude of saidpressure directed to said servo valve by said sixth conduit, a threedimensional cam member adapted to be in continuous contact with saidsecond variable orificevalve member sofas to position saidsecondvariable orifice valve'member in accordance with 'the position ofsaid cam, avtemperature responsive motor member for rotating saidcamniember-in accordance with variations in temperature,y piston meansresponsive to the speed of rotation of said compressor for positioningsaid cam mem-v ber axially in accordance therewith, manually positionedcam meanscooperatng with saidthird pressure responsivemeans for creatinga signal indicative of the requested fuel flow to said engine, andadjustably positioned stop means for determining the absolute minimumpermissible fuel flow pastsaid governor valve.

References Cited inthe file of this patent UNITED STATES PATENTS2,738,644` Alford i Mar. 20, 1956, 2,809,492 Arkawy oct. 15, 19572,939,280 Farkas June 7, 1960 2,989,849 Toren June 27, 1961 s s FOREIGNPATENTS '294,244- Australia .;--f-f .-.V-Y Aug- 91.19567, 804,702 GreatBritain Nov. 19, 1958

1. A FUEL CONTROL FOR A FREE-SHAFT TURBINE ENGINE HAVING A FREE TURBINEAND A COMPRESSOR WITH A DRIVING TURBINE THEREFOR, COMPRISING A HOUSING,AN UNMETERED FUEL INLET AND A METERED FUEL OUTLET IN SAID HOUSING, ACONDUIT CONNECTING SAID INLET AND OUTLET, A VARIABLE ORIFICE VALVEMEMBER ADAPTED TO VARIABLY RESTRICT THE FUEL FLOW THROUGH SAID CONDUITIN ACCORDANCE WITH COMPRESSOR PRESSURE, A SECOND VALVE MEMBER ADAPTED TOMETER THE FUEL FLOW THROUGH SAID CONDUIT IN ACCORDANCE WITH COMPRESSORSPEED, A PRESSURE RESPONSIVE UNMETERED FUEL BYPASS VALVE, CONDUIT MEANSDIRECTING A PRESSURE SIGNAL CREATED IN PART BY METERED FUEL PRESSURE TOSAID PRESSURE RESPONSIVE BYPASS VALVE, A SERVO VALVE ADAPTED TO AT TIMESREDUCE IN VARYING DEGREES THE MAGNITUDE OF SAID PRESSURE SIGNAL, AND AFORCE BALANCE SYSTEM RESPONSIVE TO THE FUEL FLOW PAST SAID VARIABLEORIFICE VALVE MEMBER FOR CONTROLLING THE POSITION OF SAID SERVO VALVE.